The prejunctional modulatory receptors can be new targets for pharmacological manipulation of lower urinary tract and also possible sites for pathologically-induced changes that can lead to a disruption of normal voiding function. The experiments in this proposal will evaluate two major questions. The first deals with the intracellular mechanisms (e.g., signal transduction pathways) underlying presynaptic muscarinic and adrenergic facilitation of transmitter release in the urinary bladder of rats and human. We will investigate: (1) the contribution of extracellular calcium entry via different voltage gated calcium channels to presynaptic facilitation, (2) the role of tonic G protein inhibition of calcium channels, (3) the function of intracellularly released calcium with special attention to calcium-induced calcium release, (4) the role of protein kinases and phosphatases. We will extend the investigations to the neurons of the major pelvic ganglion where both the transmitter release and the direct response of calcium channels to the facilitatory processes can be studied. The second major topic deals with the influence of pathology on presynaptic modulation. Changes in presynaptic modulation may occur in hyperactive bladders induced by spinal cord injury, by bladder hyperactivity induced by inflammation, and by aging. It is expected that the proposed experiments will provide new insights into the pathophysiologic mechanisms underlying neurogenic disorders of the bladder and may lead to new pharmacological approaches for the treatment of these disorders.